A vehicle body lateral section, for example, an automobile is provided with: plural pillars, each of which is vertically provided in a body lower structure; and a roof side rail that extends in a longitudinal direction of the vehicle to connect upper ends of the pillars. A roof is provided between the right and left roof side rails, and each of the pillars supports the roof via the roof side rail. A front pillar is often inclined rearward along an inclination of a windshield glass, and a rear pillar is often inclined forward. The front pillar, the roof side rail, and the rear pillar form an arch shape as a whole. Hereinafter, a structure that is constructed of the front pillar, the roof side rail, and the rear pillar will be described as an upper arch structure.
In the paragraph 0011 in PATENT DOCUMENT 1 below, it is introduced that in recent years a high tensile steel plate has frequently been used for a body strength member. In addition, a vehicle body lateral structure is disclosed in the paragraphs 0246 to 0262 of the same document. In the vehicle body lateral structure, a reinforcing member (70, 70-1) that is made of a high-strength steel material and has a closed cross section is arranged in an arch structure that is constructed of pillars (63, 67) and a roof side rail (65). Note that the above reference signs in the parentheses are reference signs used in PATENT DOCUMENT 1 below and are not related to reference signs used in embodiments of the present application.